The overall goal of this proposal is to develop vitamin D-based therapeutic regimens to supplement the treatment, and design strategies for the prevention, of human acute myeloid leukemia (AML). Specifically, we will focus on the identification of analogs of the physiological form of vitamin D, 1,25- dihydroxyvitamin D3 (1,25D and analogs are collectively dubbed deltanoids) which are the most effective when administered to leukemia cells in combination with Carnosic acid . We will study the alterations in gene expression, and other cellular changes that can be used as biomarkers of response to this treatment. AML cells ex vivo, freshly obtained from patients, and cells in established cultur will be used for studies of cell differentiation, resistance to differentiation, cell cycle arrest,and survival mechanisms in the presence of therapeutic toxic agents. The rationale is provided by numerous previous observations that deltanoids induce expression of genes which regulate monocytic differentiation but also can cause resistance to differentiation (Specific Aim 1), the differentiation-associated cell cycle arrest (Specific Aim 2), and cell survival changes dependent on microRNA32 and on signaling pathways that link the scaffold protein hKSR2 with NFkB complex(Specific Aim 3). Special attention will be given to deltanoids already approved for human administration the differentiation activity of which is highly enhanced by Carnosic acid. This project will be accomplished by a variety of approaches, including addition to cultured cells of pharmacological agents, antisense oligonucleotides, siRNAs, molecular decoys, and transfected plasmid constructs to study the molecular consequences of these manipulations, which will be determined by immunoblotting, quantitative RT-PCR, immunoprecipitation, and other molecular techniques. Differentiating cells will be monitored by determination of cell surface and molecular markers, as well as by the activity and the expression of various enzymes. The information obtained in basic studies will be utilized to guide development of Clinical Trials of deltanoids, and their combinations with the differentiation enhancer carnosic acid, while translational studies on leukemic cells ex vivo will serve to identify biomarkers of responsiveness to deltanoids and the recognition of subgroups of myeloid leukemias which will be the most suitable for the initiation of planned clinical trials.